1. Field of the Invention
The present invention relates to a stacked resonator with a plurality of conductors stacking one upon another.
2. Description of the Related Art
For example, demanding requirements of miniaturization and minimum loss are placed on filters used in radio communication equipments such as cellular phones. Consequently, the same is true for resonators configuring the filters. Japanese Unexamined Patent Publication No. 2003-218604 describes a stacked dielectric resonator in which a plurality of resonance electrodes are stacked so as to be comb-line coupled to each other.
FIG. 23 illustrates schematically a resonator structure when two quarter-wave (λ/4) resonators each including a TEM (transverse electro magnetic) line are comb-line coupled to each other. The term “comb-line coupling” is a method of coupling two resonators 101 and 102 so as to be electromagnetically coupled to each other by arranging so that their respective open ends 101A and 102A are opposed to each other, and their respective short-circuit ends are opposed to each other. FIGS. 24A and 24B illustrate schematically distributions of magnetic fields H in the two comb-line coupled resonators 101 and 102. Specifically, FIGS. 24A and 24B illustrate magnetic fields within a cross section orthogonal to the direction of flow of a current i in the resonators illustrated in FIG. 23. The direction of the current i in FIGS. 24A and 24B is a direction orthogonal to the drawing surface. In the two comb-line coupled resonators 101 and 102, as illustrated in FIG. 24A, the magnetic field H is distributed in the same direction (for example, in a counterclockwise direction) within the cross section. In this case, when the two resonators 101 and 102 are brought into a close relationship in the stacking direction to establish a strong comb-line coupling, the result is a magnetic field equivalent to the condition which the two resonators 101 and 102 are assumed to be a single conductor, as illustrated in FIG. 24B. This substantially increases conductor thickness. Thus, in the stacked dielectric resonator as described in the above Publication, the conductor thickness can be assumed to be increased to reduce the conductor loss by using the property that the current i flows in the same direction to each of the comb-line coupled resonators.